help needed with particle instancing based on poly normal direction.

[gdepena]

Runtime expression:

// define a variable with the particle position
   vector $p = particleShape1.position;
   
   // get surface normal at particle position
   vector $normal = `nearestPointOnMesh -ip ($p.x) ($p.y) ($p.z) -normal -q pPlane1`;
   
   // define worldUp
   vector $worldUp = <<0,1,0>>;
   
   // calculate normalized directions by which to align the y and z axis of the instance object
   vector $directionOfZaxis = unit(cross( $normal, $worldUp ));
   vector $directionOfYaxis = unit(cross( $directionOfZaxis, $normal ));
   
   // solve each angle, result in degrees
   float $rotZ = rad_to_deg(( atan2( ($normal.y), ($normal.x) ) ));
   float $rotY = rad_to_deg(( asin( -($normal.z) ) ));
   
   // feed result into the rotationPP attribute
   particleShape1.rotationPP = << particleShape1.randomRotationX, $rotY, $rotZ >>;
   

Optionally you can add the runtime expressions in the creation too.
Also, notice the “pPlane1”, which should be corrected to match the name your poly object.

ctp,

I’m trying a variation of yours but i can’t seem to get it right! I work with the Z up and thus i’m attempting to modify your code for one with the Z up.

This is the expression that i’m creating:

// sets the orient axis for the instance
particleShape1.aimUp = <<0,0,1>>;

// get surface normal at particle position
vector $particlePos = particleShape1.position;
vector $normal = nearestPointOnMesh -ip ($particlePos.x) ($particlePos.y) ($particlePos.z) -nr -q pPlane1;

// orient the instance
particleShape1.aimDir = $normal;

// random rotation for Z axis
particleShape1.randomRotationZ = rand(360);

//solve each angle, convert to degrees
float $rotX = rad_to_deg( atan2( ($normal.y), ($normal.z) ) );
float $rotY = rad_to_deg( asin( -($normal.x) ) );

// asign random rotation in Z
particleShape1.rotationPP = << $rotX, $rotY, particleShape1.randomRotationZ >>;

any help with this will be greatly appreciated, i’ve attached my file for your reference.

Thanks,

-G

[vsPiotr]

[ should have read the posts above, ignore me]

Acidream = genius.

[akewt]

hey guys

great thread and another resurrection!

so i was mucking around with YourDaftPunks scene (thanks) and stimuli’s post trying to aim the poly planes to a camera in the y axis whilst maintaning the orientation to the surface.

i am trying to replicate a ground cover system in a game engine. don’t ask why, but I am!

i think stimulis solution for aiming would break the surface orientation?

thanks for the informative read guys.

Kev

[younessama]

gotta love the undead threads

duplicate your instanced geo a couple of times and rotate them randomly in y.
freeze all transforms
instance with indexPP set to rand( 0 , numOfInstances+1 )

its kind of a cheat because the idea is to just make a connection instead of duplicating and making your scene bigger. but sometimes getting it done is more important than doing it “properly”
Just like when someone hands you a scene file with an outliner thats 5000 pages long of unnamed nodes and you dump in a new group named “screwYouUnorganizedJerk”
…or maybe its just me. haha :applause:

He can add a custom attribute randomRotation and give and give it this expression :

particleshape1.randomRotation = rand(0,0.360,0)

and map it to the rotation, like that he will get random rotation on all the instances on the Y axis.
the bad thing about doing it with Index is that more indexes in the instances effect the ram during the rendering and slow down a bit the render if the objects instances get pretty big with complicated shader network complicated .
thanks

[PurpleRainbow]

getting degrees with angleBetween command, and with random X rotation

// getting particle location
vector $p = nParticleShape1.position;

// calculating normal
vector $normal = nearestPointOnMesh -ip ($p.x ) ($p.y) ($p.z) -normal -q pSphere1;

// solving angles
float $angBet[] = angleBetween -euler -v1 1 0 0 -v2 ($normal.x)($normal.y)($normal.z);

// setting rotation with random
nParticleShape1.rotationPP = <<($angBet[0]+rand(180)), $angBet[1], $angBet[2]>>;

here your object for instancing should be heading x direction with its “up”

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